Conservation and management of rare plant species

The Tennessee coneflower is listed under the U.S. Endangered Species Act. (www.npr.org)

Over 8,000 plant species worldwide are threatened with extinction, according to the World Conservation Union, and that number grows daily. Researchers have recently estimated that between 22 and 47% of the world’s flora is in serious decline. In the United States alone, 744 plant species are federally listed as threatened or endangered by the U. S. Fish and Wildlife Service, comprising over half of all imperiled species. These are disturbing trends, because plants provide essential ecosystem services that sustain life on the planet: producing oxygen, sequestering carbon dioxide (a major greenhouse gas), and providing food, medicines, building materials, textiles, and habitat. Many plants listed as in danger are endemic (restricted in distribution) to small regions or require specialized habitats. However, an increasing number of formerly “common” or dominant species are rapidly becoming vulnerable. Thus, efforts to conserve and manage plants are critically needed around the world.

Plymouth gentian (Sabatia kennedyana) is a rare plant of the Atlantic coastal plain that depends on variation in water levels to discourage growth of competing vegetation. (Source: Elizabeth Farnsworth)

Many factors are contributing to the loss of plant species, and these threats act synergistically. Foremost among the causes of extinction is conversion or destruction of habitats by humans. Overharvesting of wild plants for medicine and food also endangers species. In the United States, over half of imperiled plant species are threatened with competition or predation by invasive exotic species. Pollution accounts for declines in still more species. It is imperative to evaluate the threats to plant species accurately and to address these threats explicitly through conservation and management.

Several approaches can help save rare plant species and protect habitat for all species generally. First, the global distribution of plant species and their conservation status must be thoroughly and systematically documented. Scientists (including botanists, taxonomists, and ecologists) are working hard to catalogue, name, and describe the biology of plants throughout the world before they disappear, often using a method called Rapid Ecological Assessment. This activity is especially important in highly diverse regions of the globe with high numbers of rare species, such as tropical and temperate rainforests, and fynbos and other species-rich ecosystems of Mediterranean and monsoonal climates. Until the past few decades, many of these areas have remained extremely remote and relatively difficult for people to access and settle; however new technologies and population pressures are allowing people to colonize these regions and to permanently alter their ecology, even as scientists work to discover their biological richness.

Wiliwili seeds Erythrina sandwicensis (http://www.usbg.gov/gardens)
Second, global efforts are underway to protect the remaining areas on earth that harbor high diversity of both common and rare plants(so-called biodiversity hotspots). The goal is to provide habitat in perpetuity for as many species of plants, animals, and other organisms as possible within a given area. Protection involves setting aside large, relatively intact tracts of land to reduce access and prevent exploitation by humans. Governments and international or regional conservation organizations frequently work together to acquire this land and to regulate human uses of it. However, these protection projects are often hampered by lack of funds, lack of political will, and a lack of understanding by the populace as to why such conservation is needed when it conflicts with human needs and goals. Thus, many of these areas are regarded and treated as “parks on paper,” and incursions continue unabated.

A third approach, therefore, is to educate people about the economic, utilitarian, and intrinsic values of biodiversity. Many efforts to date have focused on educating local people about rare species and engaging them in helping to enforce the boundaries of protected areas. Local populations already often possess in-depth knowledge about the uses of wild plants and the need to utilize these resources wisely, but they are pressured by growing populations, poverty, and forces such as war and natural disasters that displace them to new areas or induce them to overharvest or destroy habitats. Likewise, even affluent or highly-educated landowners or politicians purposely or incidentally endanger plant populations when the promise of wealth outweighs the perceived benefits of protecting rare species or when their rights to use private land appear to be constrained. Outreach is needed to change these perceptions, and many conservation organizations now engage a wide array of stakeholders as soon as they begin to formulate conservation plans.

Fourth, national and international legislation is necessary to prevent the trafficking of rare species such as orchids. For example, the Convention on International Trade in Endangered Species of Wild Flora and Fauna (CITES); prohibits or limits trade of almost 28,000 species of rare plants worldwide.

Mammillaria hahniana (Old woman cactus) (http://www.usbg.gov/gardens)
Even if critical habitat for rare plant species is successfully protected, ecological processes continue to affect the survival and future viability of populations. A fifth component of the conservationist’s toolkit, therefore, is active management of these processes. Globally, perhaps the most important of these factors is global climate change. Plants are very sensitive to drought, storms, and temperature extremes, all of which are predicted by the Intergovernmental Panel on Climate Change (IPCC) to increase in severity in the coming decades as the earth’s climate warms (there is uncertainty about exactly where and when these changes will take place, but a high probability of significant disruptions to regional climate if current emissions trends continue). The geographical ranges of plant species have shifted widely in the past in response to glaciation and warming events, and will do so in the future. But their ability to move is constrained by their own adaptability and by the availability of suitable new habitat. For example, alpine plant communities, in which species are adapted to long winters with abundant snowfall, may disappear completely in some areas as mountainglaciers recede, snowfall amounts decrease, and plants acclimated to warmer climates move in and outcompete them. Rising sea levels also threaten to inundate coastal plant communities such as mangroves and salt marshes. Humans are also exerting other large-scale changes that threaten plant species; atmospheric pollutants such as nitrogen compounds (from automobiles and fertilizers) and clorofluorocarbons (refrigerants and aerosols) are contributing to acid rain and increased ultraviolet radiation due to the thinning of the earth’s protectant ozone layer, respectively. Solving these global-scale problems in order to conserve plants and other species will demand coordinated efforts on the part of all people worldwide.

Many rare plant species have evolved specialized adaptations that depend on natural disturbance processes to maintain open habitats or to provide periodic flushes of water and nutrients, and these species become rarer when these processes are disrupted. Plant communities such as prairies and sandplain grasslands, for example, benefit from occasional wildfires that stimulate seed germination and eliminate competing species. People have suppressed many of these disturbances to avert their dangerous impacts on lives and property – preventing burning or diverting and damming rivers to preclude floods. Therefore, many rare plant communities need to be actively managed in ways that mimic or restore some of these critical processes. For example, conservation managers now have to set localized, controlled burns in order to maintain fire-dependent plant communities. Such techniques are labor-intensive, expensive, and sometimes controversial.

The fynbos (fine bush) vegetation of South Africa is exceptionally rich in plant species that are found nowhere else on earth. It is the focus of concerted conservation efforts. (Source: Elizabeth Farnsworth)
Today’s threats may abate tomorrow, creating opportunities for plants to “wait-it-out” or recolonize and reclaim their former habitats. Fortunately, many plant species possess a unique strategy for coping with stressful environments in the long-term: the seed or spore. Seeds and spores of a wide variety of species can go dormant for long periods (weeks up to centuries), postponing development of the plant embryo until external cues indicate that the environment is optimal for survival. Conservation organizations take advantage of this capacity by collecting seeds and spores from rare plant populations and storing them in a seed bank over the long term. Successful storage demands an understanding of the unique physiological tolerances of each species and their capacity to undergo and recovery from dormancy. Perhaps the world’s most ambitious seed storage project is the Millennium Seed Bank of the Royal Botanical Gardens at Kew, which seeks to collect and store genetically diverse representatives of 10% of earth’s plant species over the next decade. Although seed banks can provide an insurance policy against extinction for certain species, other taxa produce seeds that cannot tolerate storage. Sometimes the leaf or root tissues of these plants can be deep-frozen and reconstituted; other times the species must be maintained and propagated in living collections in botanical gardens, much as endangered animals are housed in zoos. Thus, botanical gardens can be critical repositories of biodiversity, as well as aesthetically pleasing and educational institutions for the public to enjoy.

Reintroduction or creation of new populations of plants is another conservation tool that follows on seedbanking, but this practice carries its own challenges. Many reintroduction efforts fail because the species’ ecology is poorly understood or because their original habitat has been irrevocably damaged. It is risky to existing populations to remove and deplete their seeds in favor of establishing new populations. It is not enough to scatter seeds in apparently appropriate habitat and hope for the best. Seedlings must be monitored closely for survival and reproduction, and reasons for plant mortality must be carefully evaluated. Thus, introduction projects are usually undertaken only when no other alternative for saving the species in situ is available and when the probability of long-term success is demonstrably high. Reintroduction is not a substitute for proactive habitat protection, nor can it mitigate for the destruction of existing populations.

The issues facing rare plants are formidable, and many species have already been lost. But the news is not all bad: efforts to save species are resulting in many successes. In 2003, the first plant ever was removed from the U. S. Fish and Wildlife Service’s Endangered Species list due to cooperative efforts by the Service and the New England Wild Flower Society. The diminutive Robbins’ cinquefoil, restricted to a handful of alpine communities in northern New Hampshire, had suffered for years from trampling and other threats. Botanists learned how to propagate the plant from seed, and introduced two new populations into the plant’s native habitat in the White Mountains. At the same time, a popular trail that led directly through the existing populations of beleaguered plants was relocated. Today, the plants are thriving and the species is considered secure. Increased understanding of species’ requirements, activities to reduce threats, and far-sighted and collaborative strategies to save populations and habitats will help to stem the tide of plant extinction in the future.